One of the recent services in the railway transportation services is a passenger information service available in the vehicles. For this purpose, a new communication cable is set along the railway and display panels are installed on the upper site of the car doors. In most cases, the information is provided by playback operation of the data that is retrieved from storage devices installed in the cars, but it is not on-line or real-time information. A recent demand for the technology is to provide the up to date information through a communication system that makes a linkage between the railway vehicles and the railway service facilities (we call this communication system as “a railway vehicle-facility intra communication system” or an intra communication system for an abbreviation). There are a couple of conventional technologies for such demand as shown in the reference 1 and 2. The technology described in the reference 1 describes a communication technology using a power line carrier with modulator and demodulator devices installed in the cars and railway power stations where the communication is done through the trolley wires. The technology in the reference 2 describes a communication services by which a passenger can place commercial orders during when he is traveling by the train.
Reference 1:                Published Japanese Patent Application: Paragraph 0005 -0015, JP, H11-317697, A (1999)        
Reference 2:                Published Japanese Patent Application: Paragraph 0005-0012 JP, 2002-215914, A (2002)        